TL;DR: If modeling with Blender, use the triangulate modifier to reduce the likelihood of SFM messing up your models.

I already posted this tutorial in the Open Source Filmmaker forums, but I thought I could also share this tutorial here on the Blender forums.

I had a bizarre compiling issue involving a model of a bench I was working on in Blender. My bench, a curved shaped bench, looked like this in Blender:
http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1158252859

However, after compiling the model, the bench proceeded to look like this monstrosity in SFM:
http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1158253282
http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1158254051

It turns out that Source Filmmaker had converted the Blender models from quads to triangles, resulting in these unsightly flaps coming off the bench.

To correct this weird error, you simply need to use the triangulate modifier[docs.blender.org] on your mesh. After using the triangulate modifier, this is how my bench looks like in Blender:
http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1158269782

And this is how the curved bench looks like in SFM:
http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1158278506